Transmission circuits



June 12, 1928. 1,672,968

H. A. WHITEHOBN TRANSMISSION cIRcfJITs Filed Deg. 50, 1922 hvenfonhomer A. W/mehorn.

Patented June 12, 1928.

UNITED STATES PATENT OFFICE.

HOMER A. WHITEHORN, 0] PORT WASHINGTON, NEW YORK, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TRANSMISSION CIRCUITS.

Application filed December 30, 1922. Serial). 609,881.

This invention relates totransmission circuits and particularly to coupling means for circuits having different impedance characteristics.

An object of the invention is a coupling means for circuits having different charac-v terist ic impedances which vary differently with frequency.

In accordance with the preferred form of the invention there is provided, between two circuits possessing different characteristic impedances, a coupling consisting of a condenser shunted by a transformer having a high mutual impedance and an inductance. In the case of high frequency currents the condenser acts as the main coupling medium between the two circuits, and in order to insure that the high frequency currents pass through the condenser the inductance coil is connected in bridge of the circuits while the transformer serves as a coupling means for the low fre uency currents. It willbeapparent from t e description hereinafter that a coupling means is provided whereby substantially no transition or reflection losses occurs in the transmission of currents from one circuit to another.

A better understanding of the invention may be had from the following description taken in conjunction with the accompanying drawings, wherein Fig. 1 illustrates a coupling means between a vacuum tube and a telephone receiver. Fig. 2 shows a coupling means for connecting circuits possess ing impedances which differ with different frequencies, while Fig. 3 illustrates a modification of the arrangement of Fig. 2.

Referring now to the drawing,-there is shown in Fig. l a vacuum tube amplifier or detector 5 having its output circuit coupled with a telephone receiver 6 by means of a coupling 7. The receiver 6.has .its operating magnet wound to have an impedance substantially equal to that of the vacuum tube at the upper part of the frequency range to be transmitted, fonexample the voice range. Now to prevent the introduction of transition or reflection losses when currents of frequencies in the lower part of the range to be transmitted are impressed on the receiver, the coupling 7 is provided. This coupling is made up of a condenser 8 having a terminal connected to the output circuit of the tube 5, while the other terminal is connected to the receiver 6, a transformer 9 having a high mutual impedance in shunt of the condenser and an inductance 10 in the shunt path with the transformer 9 to compel the high frequency currents to pass through the condenser 8. The input circuit of the tube 5 being connected to the transformer 11 which receives the currents to be detected or amplified,.currentsof a frequency depending on the frequency of the received currents will be impressed on the receiver 6.

With the impedance of the receiver 6 equal to that of the output circuit of the tube 5 for the higher frequency range, maximum transfer of energy would result for such frequency range if the receiver 6 were directly coupled with the output circuit of tube 5. However, at the lower-frequencies of the impressed current, without a coupling means such as 7, detrimental transition or reflection losses would result in the transmission of currents from one circuit to the other, since the impedance of the receiver 6 is lower at the lower frequencies. This condition is obviated in the present invention by the introduction of the coupling 7 wherein the condenser 8 serves as a coupling medium between the two circuits at the higher frequencies, the currents of these frequencies being prevented from passing through the transformer 9 by the use of the inductance coil 10, which, in this particular case, serves as a choke or retard coil. Now in the case of low frequency currents, the impedance of the receiver is stepped up by the transformer to match the impedance of the vacuum tube. Accordingly, the transformer 9 for this condition serves as the coupling means for the two circuits.

In a co ending application, Serial No. 485,447, fied July 18, 1922, a coupling means is disclosed for coupling circuits which have different impedance at different frequencies whereby substantially no transition or reflection losses results when lines having different impedances at'higher frequencies and the same impedance at the lower frequencies are connected. Fig. 2 illustrates a system of connection embodying the principle of the above referred to application in addition to the provision of a coupling for circuits having the same impedance at the higher frequency but differing at the lower frequencies. Thus, with the combination of the two a system of coupling is provided whereby for a wide range of frequencies, both above and below the frequency at which the circuits are naturally matched, impulses may be transmitted between the two types of circuits without suffering any substantial transition or reflection losses.

As shown in Fig. 2, a unit 12 comprising capacitance and resistance is connected to the terminals 13 and 14. It is understood, of course, that the unit 12 re resents the equivalent of a cable circuit. 0 the ri ht 0 Fig. 2 there is shown a unit 15.embo ying inductance and resistance. Thislatter unit is the equivalent of the usual telephone receiver. It is to be noted here, however, that the impedance of the unit 12 decreases with increase in frequency, 'while for the unit 15 the opposite conditions results, that is, the impedance increa-ijes with increase in frequency. In order that currents may be impressed from one circuit to the other without suffering any appreciable transition or reflection losses for all frequencies, two types of couplers are employed. One of these couplers comprises a transformer 18 having two windings, the terminal 'of one winding being connected to the junction point 13, a terminal of the other winding bein connected to the unit 15. The other terminal of each of the windings composing the transformer 18 are connected to a plate of a condenser 19 which has its other plate connected to the other side ofthe circuit. The second coupler is the same as the one described in connection with Fig. 1 and comprises a condenser 20 shunted by a transformer 21 having a high mutual impedance, and an inductance coil 22 which is connected in a shunt path between the transformer21 and the same side of the circuit to which the one terminal of the condenser 19 is connected.

For high frequency currents, such as for example 10,000 to 30,000 cycles, condenser 19 is of a negligible impedance so that transformer-18 serves as if it were directly connected between the points 13 and 14. However, for the opposite condition,,that isfor currents in the neighborhood of the frequency at which the interconnected circuits are naturally matched, the condenser 19 will offer appreciable impedance to the currents so that substantially all of these currents flow through the windings of the transformer 18. which being a low mutual transformer offers very little impedance to their flow. Up to this point the currents have suffered substantially no transition or reflection losses. However, since the circuit is coupled with a unit, the impedance of which increases with increase in frequency and vice versa, it is necessary to further insure that the currents will sufl'er no a-p neciable transition or reflection 1m." 0' provide for this the invention, as shown in Fig. 2, utilizes an arrangement similar to that described in connection with Fig. 1. In the case of the higher frequency currents, the

condenser 20 short-circuits the transformer 21 and thus serves as the main coupling between the two circuits. It is tc be noted here also that the high frequency currents are compelled to pass through the condenser 20 by the provision of the inductance coil 22which serves as a retard or choke coil for the high frequency currents. Now, in the case of the lower frequency currents, the impedance of the condenser 20 increasesto a point such that the transformer 21 acts as the main coupling between the two circuits. It is apparent from the previous description that by the use of the two types of coupling means a system is provided whereby currents may be transmitted from circuits having difi'erent impedance characteristics for difl'erent frequencies without substantial transition or reflection losses.

'lhe modification illustrated in Fig. 3 is the same as that of Fig. 2, except that in place of the transformer 18 an auto-transformer 23 is provided. Likewise, in the case of the transformer 21 of Fig. 2, an autotranst'ormer 24 is shown connected with the respective circuits, as in Fig. 3. The ration of the arrangement of Fig. 3 is identical to that of Fig. 2, with the exception of the transformation action of the transformers. It is thought that further description of this modification is unnecessary. In allthe figures the transformer windings preferably have the directions shown in the drawings.

Although the invention has been disclosed and described in connection with particular types of circuits, it is, of course, obvious that variations may be made without departing from the spirit and scope of the present invention. 1 or example, in certain cases the inductance 10 may be unnecessary.

What is claimed is:

1. In combination, two circuits having different impedance characteristics for difierent frequencies, a plurality of couplers between said circuits, each of said couplers comprising a transformer havin two windings, the windings of each trans ormer having one lead in common, a'condenser connected in shunt to both windings of one of said transformers, and a second condenser connected in the circuit of the common lead of the windings of the other transformen.

2. In combination, two circuits havin different impedance characteristics for di erent frequencies a pair of couplers between said circuits arranged to respond differently tov different frequencies, one of said couplers comprising a transformer having its windings connected serially with saidcircuits, and a condenser connected between the junction point of said windings and the other side of said circuits, the other of said couplers being composed of a transformer shunted by a condenser and connected serially with said circuits, and an inductance connected between the transformer and the other side of said circuit.

3. In combination, two transmission circuits the impedances of which are substantially equal at one frequency to be transmitted and substantially different at another frequency to be transmitted, and coupling means for said circuits comprising a non unity ratiotransformer with primary and secondary windings for matching said impedances at said second frequency and a path of low impedance at the first frequency in shunt to both windings of said transformer to transmit waves of said first frequency.

4. A combination according to claim 3 and a path of high impedance at the first fre-' quenc in series with both windings of said trans orrner.

5. An electric circuit for joining two circuits havin different frequency-impedance characteristics to prevent substantially any reflection loss for a. wide range of frequencies transmitted comprising an impedance transformin to substantia ly match the impedance of said circuits for frequencies in the lower portion of said range and connectedso as to couple said circuits for said frequencies, and means for directly connecting said circuits for frequencies in the uper portion of said range, said last mentioned means comprising a condenser connected in shunt to said impedance transforming means.

In witness whereof, I hereunto subscribe my name this 28th day of December A. D. 1922.

HOMER A. .WHITEHORN.

means having such a ratio as a 

